1. Field of the Invention
This invention relates to pesticide compositions, and more specifically to a process for improving the storage stability of neem seed extracts which contain azadirachtin as the active pesticidal ingredient by contacting the extracts with an adsorbent capable of selectively removing water.
2. Description of the Prior Art
The biological activities of the neem tree seeds have long been recognized. Of primary importance are the potent pesticidal properties of azadirachtin, the main active ingredient in the neem seed. Azadirachtin is a tetranortriterpenoid that causes feeding inhibition and growth disruption in various insect, mite, nematode, etc. orders.
There are various methods known in the prior art to extract azadirachtin from neem seeds. Typically, these methods involve drying the neem seeds, milling the dried seeds to a coarse powder, and extracting the powder with various solvents such as methanol, ethanol, water, methylene chloride, chloroform, hexane, methylethylketone, butanol, petroleum benzene, ether, acetone, methyl tertbutyl ether, diethylcarbonate, etc. In general, it has been found that the efficiency of the extract yield can be increased by increasing the solvent polarity, i.e., from hexane to ethanol, ethanol to methanol, methanol to water, etc. However, despite the initial drying of the neem seeds, they still contain between 6 to 15% water. Thus, while the utilization of more polar solvents will increase the extraction efficiency relative to azadirachtin, it will also extract more of the water contained within the neem seeds and results in aqueous-containing extracts. That is, since water and azadirachtin have similar solubilities, the solvents useful for extracting the azadirachtin from neem seeds also extract any water contained therein. Crude neem seed extracts will typically contain up to 20% water. It now has been discovered that the presence this high concentration of water in neem seed extracts is a primary cause of the degradation of azadirachtin in solution.